Centrifugal blasting machines are commonly used in the art to strip or clean metal castings and other items. Centrifugal blasting machines typically employ a throwing wheel assembly comprising a plurality of throwing elements, referred to as throwing blades, mounted on the face of a rotator, runnerhead, or other rotatable wheel element. The throwing blades are adapted for receiving a stream of abrasive particulate material and throwing the particulate material radially outward from the wheel at an appropriate discharge point.
Because of the action of the abrasive material within the centrifugal blasting apparatus, the throwing blades will commonly undergo considerable wear and must be replaced periodically. To avoid having to replace the entire throwing wheel assembly, the blades must be removably mounted on the throwing wheel. Unfortunately, in order to provide a sufficiently secure attachment for the blasting operation, the blade attachment assemblies used heretofore typically have not allowed the blade elements to be quickly and easily removed and replaced. The removal and replacement of the blade elements often requires special tools, as well as the extensive disassembly of other parts of the device.
A more recent prior art throwing wheel assembly 10 which both (a) provides for the secure attachment of the blades to the throwing wheel and (b) allows the blades to be quickly removed and replaced, is depicted in FIGS. 1–4. The prior art assembly 10 can be used with any length or width of blade, does not require the machining and close tolerances characteristic of previous devices, reduces the number of costly machined parts required for attaching the blades, allows the use of bi-directional throwing blades, and requires no tools for removing or installing the blades.
The prior art assembly 10 comprises: a throwing wheel 13 having an axis of rotation 11; a hub or rotor 12 affixed to throwing wheel 13; a plurality of throwing blades 14 which are removably mounted on, and are perpendicular to, the face 9 of throwing wheel 13; and an impeller 23 centrally mounted on hub 12 between the inlet ends 16 of the throwing blades 14. The blades 14 generally extend radially away from the impeller 23.
The impeller 23 is rotatably affixed to hub 12 for receiving a stream of abrasive particulate blasting material from a spout 20 and feeding the abrasive material to the throwing blades 14. The impeller 23 is provided with openings 24 for delivering the abrasive material through a discharge opening 25 provided in the impeller case 21. The abrasive material is received on the inlet ends 16 of the blades 14 as the blades 14 rotate past the opening 25. The abrasive material moves outwardly along the throwing surface 15 of the blade 14 and is thrown from the distal end 17 of the throwing surface 15 at a desired discharge point.
Each of the throwing blades 14 comprises: an inner lateral side 30 positionable on the face 9 of wheel 13; an outer lateral side 29 opposite side 30; a first holding structure 26 which projects laterally outward from the lower end of side 30; and a second holding structure 27 which projects laterally outward from the upper portion of side 30. The blade 14 is a one-piece component with holding structures 26 and 27 being integral features thereof. The upper holding structure 27 is a rigid lug or arm which is receivable in a corresponding detent 40 provided in the periphery of the throwing wheel 13. A bore 45 extends radially inward from detent 40 for receiving a spring or other biasing element 95. The upper holding structure 27 includes a cavity or recess 90 in the bottom thereof for receiving and engaging the upper end of the biasing element 95.
The lower holding structure 26 of blade 14 includes outer lip portions 50 which hook or project upwardly toward the upper discharge end 17 of the blade 14 and are adapted to engage corresponding counter lip structures 51 formed in the face 9 of wheel 13. The counter lip structures 51 are contained within a lower detent 53 formed in face 9. The biasing element 95 continuously acts against the upper holding structure 27 to urge the blade 14 radially outward so that the lips 50 or other locking features of the lower holding structure 26 are held in locking engagement with the corresponding lips 51 or other locking features provided detent 53.
In the prior art assembly 10, each blade 14 can be easily attached to the throwing wheel 13 by placing the upper holding structure 27 in one of the outer detents 40, pushing the blade downward to compress the biasing element 95, pivoting the bottom of the blade 14 inward to place the lower holding structure 26 in the detent 53 and to align locking features 50 with locking features 51, and then releasing the compressive force applied to biasing element 95 so that the biasing element 95 acts to urge the blade 14 radially outward to thereby hold the lower holding structure 26 in locked engagement with the wheel 13. The blade 14 can be easily removed from wheel 13 by simply reversing this procedure.
Thus, the locking mechanism of the prior art assembly 10 holds the blades 14 securely during operation but allows the blades to be quickly and easily removed and replaced without the use of special tools and without any significant disassembly of the blasting machine. Unfortunately, however, the lower detents 53 and/or the locking features 51 formed in the face 9 of wheel 13 for receiving and retaining the lower holding structure 26 of blades 14 are exposed to significant abrasive contact and can be highly susceptible to wear. Whenever significant erosion at one or more of these attachment sites occurs, the entire throwing wheel 13 must be replaced.
Consequently, a need exists for an improved throwing wheel assembly which provides all of the benefits of the prior art assembly 10 but alleviates the wheel erosion problems. A need particularly exists for an improved throwing wheel assembly of this type which would further extend the life and reduce the cost of the wheel, eliminate the need to perform extensive millwork on the wheel, and allow the wheel to be formed from materials which are more highly abrasion resistant.